moss & fern notes b1 The haploid gametophyte stage contains half the chromosome number & produces gametes (egg & sperm) Gametophyte stage is dominant in the moss's life cycle Gametophytes are photosynthetic & have root-like rhizoids The diploid sporophyte has a complete set of chromosomes & produces spores by meiosis Sporophyte of a moss is smaller than, & attached to the Gametophyte Sporophytes lack chlorophyll & depend on the photosynthetic gametophyte for food Sporophyte has a long, slender stalk topped with a capsule Capsule forms haploid (n) spores Moss Capsules Sexual Reproduction in Moss: Mosses produce 2 kinds of gametes (egg & sperm) Gametes of Bryophytes are surrounded by a jacket of sterile cells that keep the cells from drying out Female gametes or eggs are larger with more cytoplasm & are immobile Flagellated sperm must swim to the egg through water droplets for fertilization Moss gametes form in separate reproductive structures on the Gametophyte --- Archegonium & Antheridium Archegonium Each Archegonium forms one egg, but each An

theridium forms many sperm Fertilization can occur only after rain when the Gametophyte is covered with water Sperms swim to the egg by following a chemical trail released by the egg A zygote (fertilized egg) forms that undergoes mitosis and becomes a Sporophyte Cells inside mature Sporophyte capsule undergoes meiosis and form haploid spores Haploid spores germinate into juvenile plants called protonema Protonema begin the Gametophyte generation Protonema Spores are carried by wind & sprout on moist soil forming a new Gametophyte Asexual reproduction in Mosses: Asexual reproduction in moss may occur by fragmentation or gemmae Pieces of a Gametophyte can break off & form new moss plants (fragmentation) Gemmae are tiny, cup shaped structures on the Gametophytes Raindrops separate gemmae from the parent plant so they can spread & form new Gametophytes Gemmae cups Serve as pioneer plants on bare rock or ground Help prevent erosion Alternates between dominant Sporophyte stage & Gametophyte stage Sporophyte stage has true roots, stems, & leaves Produce spores on the underside of leaves Leaves are

 called fronds & are attached by a stem-like petiole FERNS Spores produced on underside of fronds in clusters of sporangia called sori Spores undergo meiosis, are spread by wind, & germinate on moist soil to form prothallus Prothallus begins the Gametophyte stage Mature Gametophytes are small, heart-shaped structures that live only a short time Male antheridia & female archegonia grow on the prothalli Sperm must swim to the egg to fertilize it & developing embryo becomes the Sporophyte generation Newly forming fronds are called fiddleheads & uncurl Uses for Ferns: SparkNotes: The Life Cycle of Plants: Alternation of Generations Alternation of Generations The Life Cycle of Plants ← Terms Problems All plants undergo a life cycle that takes them through both haploid and diploid generations.

The multicellular diploid plant structure is called the sporophyte, which produces spores through meiotic (asexual) division. The multicellular haploid plant structure is called the gametophyte, which is formed from the spore and give rise to the haploid gametes. The fluctuation between these diploid and haploid stages that occurs in plants is called the alternation of generations. The way in which the alternation of generations occurs in plants depends on the type of plant. In bryophytes (mosses and liverworts), the dominant generation is haploid, so that the gametophyte comprises what we think of as the main plant. The opposite is true for tracheophytes (vascular plants), in which the diploid generation is dominant and the sporophyte comprises the main plant. Bryophyte Generations Bryophytes are nonvascularized plants that are still dependent on a moist environment for survival (see Plant Classification, Bryophytes . Like all plants, the bryophyte life cycle goes through both haploid (gametophyte) and diploid (sporophyte) stages.

The gametophyte comprises the main plant (the green moss or liverwort), while the diploid sporophyte is much smaller and is attached to the gametophyte. The haploid stage, in which a multicellular haploid gametophyte develops from a spore and produces haploid gametes, is the dominant stage in the bryophyte life cycle. The mature gametophyte produces both male and female gametes, which join to form a diploid zygote. The zygote develops into the diploid sporophyte, which extends from the gametophyte and produces haploid spores through meiosis. Once the spores germinate, they produce new gametophyte plants and the cycle continues. Tracheophyte Generations Tracheophytes are plants that contain vascular tissue; two of the major classes of tracheophytes are gymnosperms (conifers) and angiosperms (flowering plants). Tracheophytes, unlike bryophytes, have developed seeds that encase and protect their embryos. The dominant phase in the tracheophyte life cycle is the diploid (sporophyte) stage.

The gametophytes are very small and cannot exist independent of the parent plant. The reproductive structures of the sporophyte (cones in gymnosperms and flowers in angiosperms), produce two different kinds of haploid spores: microspores (male) and megaspores (female). This phenomenon of sexually differentiated spores is called heterospory. These spores give rise to similarly sexually differentiated gametophytes, which in turn produce gametes. Fertilization occurs when a male and female gamete join to form a zygote. The resulting embryo, encased in a seed coating, will eventually become a new sporophyte. Figure %: Gymnosperm Life Cycle Biological Diversity 5 The Sphenophyta | The Ferns | Learning Objectives | Terms | Review Questions | Links The plant kingdom contains multicellular phototrophs that usually live on land. The earliest plant fossils are from terrestrial deposits, although some plants have since returned to the water. All plant cells have a cell wall containing the carbohydrate cellulose , and often have plastids in their cytoplasm. The plant life cycle has an alternation between haploid ( gametophyte ) and diploid ( sporophyte ) generations.

There are more than 300,000 living species of plants known, as well as an extensive fossil record. Plants divide into two groups: plants lacking lignin -impregnated conducting cells (the nonvascular plants) and those containing lignin-impregnated conducting cells (the vascular plants). Living groups of nonvascular plants include the bryophytes : liverworts, hornworts, and mosses. Vascular plants are the more common plants like pines, ferns, corn, and oaks. The phylogenetic relationships within the plant kingdom are shown in Figure 1. Figure 1. Phylogenetic reconstruction of the possible relationships between plant groups and their green algal ancestor. Note this drawing proposes a green algal group, the Charophytes, as possible ancestors for the plants. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Evolution of Plants | Back to Top Fossil and biochemical evidence indicates plants are descended from multicellular green algae. Various green algal groups have been proposed for this ancestral type, with the Charophytes often being prominently mentioned.

Cladistic studies support the inclusion of the Charophytes (including the taxonomic order Coleochaetales) as sister taxa to the land plants. Algae dominated the oceans of the precambrian time over 700 million years ago. Between 500 and 400 million years ago, some algae made the transition to land, becoming plants by developing a series of adaptations to help them survive out of the water. Table 1. Photosynthetic pigments of algae and plants. Prokaryote groups are shown in red, protists in blue, and vascular plants in purple.

Taxonomic Group chlorophyll a, chlorphyll b, carotenoids Red Algae (Rhodophyta) chlorophyll a, phycocyanin, phycoerythrin, phycobilins Brown Algae (Phaeophyta) chlorophyll a, chlorphyll c, fucoxanthin and other carotenoids Golden-brown Algae (Chrysophyta) chlorophyll a, chlorphyll c, fucoxanthin and other carotenoids Dinoflagellates (Pyrrhophyta) chlorophyll a, chlorphyll c, peridinin and other carotenoids Vascular Plants chlorophyll a, chlorphyll b, carotenoids Vascular plants appeared by 350 million years ago, with forests soon following by 300 million years ago. Seed plants next evolved, with flowering plants appearing around 140 million years ago. This pattern is shown in Figure 2. Figure 2. The fossil records of some protist and plant groups. The width of the shaded space is an indicator of the number of species.

Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. The Plant Life Cycle | Back to Top Plants have an alternation of generations: the diploid spore-producing plant (sporophyte) alternates with the haploid gamete-producing plant (gametophyte), as shown in Figure 3. Animal life cycles have meiosis followed immediately by gametogenesis. Gametes are produced directly by meiosis. Male gametes are sperm. Female gametes are eggs or ova. Figure 3. Typical alternation of generations life cycle, such as occur in some protistans and plants. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. The plant life cycle has mitosis occurring in spores , produced by meiosis, that germinate into the gametophyte phase. Gametophyte size ranges from three cells (in pollen ) to several million (in a "lower plant" such as moss).

Alternation of generations occurs in plants, where the sporophyte phase is succeeded by the gametophyte phase. The sporophyte phase produces spores by meiosis within a sporangium . The gametophyte phase produces gametes by mitosis within an antheridium (producing sperm) and/or archegonium (producing eggs). These different stages of the flowering plant life cycle are shown in Figure 4. Within the plant kingdom the dominance of phases varies. Nonvascular plants , the mosses and liverworts, have the gametophyte phase dominant. Vascular plants show a progression of increasing sporophyte dominance from the ferns and "fern allies" to angiosperms. Figure 4. The life cycle stages of a flowering plant. The above image is reduced from gopher://wiscinfo.wisc.edu:2070/I9/.image/.bot/.130/Angiosperm/Angiosperm_life_cycle . Follow that link to view a larger image. Homospory and Heterospory Plants have two further variations on their life cycles.

Plants that produce bisexual gametophytes have those gametophytes germinate from isospores (iso=same) that are about all the same size. This state is referred to as homospory (sometimes referred to as isospory). A generalized homosporous plant life cycle is shown in Figure 5. Homosporous plants produce bisexual gametophytes. Ferns are a classic example of a homosporous plant. Figure 5. A typical homosporous life cycle. Note the production of a single type of bisexual gametophyte that will eventually produce the antheridia (sperm bearing structures) and archegonia (egg bearing structures). Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Plants that produce separate male and female gametophytes have those gametophytes germinate from (or within in the case of the more advanced plants) spores of different sizes (heterospores; hetero=different). The male gametophyte produces sperm, and is associated with smaller or microspores .

The female gametophyte is associated with the larger or megaspores . Heterospory is considered by botanists as a significant step toward the development of the seed. A generalized heterosporous life cycle is shown in Figure 6. Figure 6. Typical heterosporous life cycle. Note the production of separate, unisexual male and female gametophytes. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Plant Adaptations to Life on Land | Back to Top Organisms in water do not face many of the challenges that terrestrial creatures do. Water supports the organism, the moist surface of the creature is a superb surface for gas exchange, etc. For organisms to exist on land, a variety of challenges must be met. Drying out. Once removed from water and exposed to air, organisms must deal with the need to conserve water.

A number of approaches have developed, such as the development of waterproof skin (in animals), living in very moist environments (amphibians, bryophytes), and production of a waterproof surface (the cuticle in plants, cork layers and bark in woody trees). Gas exchange. Organisms that live in water are often able to exchange carbon dioxide and oxygen gases through their surfaces. These exchange surfaces are moist, thin layers across which diffusion can occur. Organismal response to the challenge of drying out tends to make these surfaces thicker, waterproof, and to retard gas exchange. Consequently, another method of gas exchange must be modified or developed. Many fish already had gills and swim bladders, so when some of them began moving between ponds, the swim bladder (a gas retention structure helping buoyancy in the fish) began to act as a gas exchange surface, ultimately evolving into the terrestrial lung. Many arthropods had gills or other internal respiratory surfaces that were modified to facilitate gas exchange on land. Plants are thought to share common ancestry with algae. The plant solution to gas exchange is a new structure, the guard cells that flank openings ( stomata ) in the above ground parts of the plant.

By opening these guard cells the plant is able to allow gas exchange by diffusion through the open stomata. Support. Organisms living in water are supported by the dense liquid they live in. Once on land, the organisms had to deal with the less dense air, which could not support their weight. Adaptations to this include animal skeletons and specialized plant cells/tissues that support the plant. Conduction. Single celled organisms only have tyo move materials in, out, and within their cells. A multicellular creature must do this at each cell in the body, plus move material in, out, and within the organism. Adaptations to this include the circulatory systems of animals, and the specialized conducting tissues xylem and phloem in plants. Some multicellular algae and bryophytes also have specialized conducting cells. Reproduction. Organisms in water can release their gametes into the water, where the gametes will swim by flagella until they ecounter each other and fertilization happens. On land, such a scenario is not possible.

Land animals have had to develop specialized reproductive systems involving fertilization when they return to water (amphibians), or internal fertilization and an amniotic egg (reptiles, birds, and mammals). Insects developed similar mechanisms. Plants have also had to deal with this, either by living in moist environments like the ferns and bryophytes do, or by developing specialized delivery systems like pollen tubes to get the sperm cells to the egg. Bryophytes | Back to Top Bryophytes are small, nonvascular plants that first evolved approximately 500 million years ago. The earliest land plants were most likely bryophytes. Bryophytes lack vascular tissue and have life cycles dominated by the gametophyte phase, as shown in Figure 7. The lack of conducting cells limits the size of the plants, generally keeping them under 5 inches high. Roots are absent in bryophytes, instead there are root-like structures known as rhizoids . Bryophytes include the hornworts, liverworts, and mosses. Figure 7. The moss life cycle. The haploid gametophyte phase is free-living and photosynthetic.

The diploid sporophyte grows from and is nourished by the gametophyte. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Tracheophytes: The Vascular Plants | Back to Top The vascular plants have specialized transporting cells xylem (for transporting water and mineral nutrients) and phloem (for transporting sugars from leaves to the rest of the plant). When we think of plants we invariably picture vascular plants. Vascular plants tend to be larger and more complex than bryophytes, and have a life cycle where the sporophyte is more prominent than the gametophyte. Vascular plants also demonstrate increased levels of organization by having organs and organ systems. The novel features oif the vascular plants are summarized in Table 2. Table 2. Major evolutionary advances of the vascular plants.

Advance Development of the root-stem-leaf vascular system nonvascularized body (thallus) that may be variously shaped no levaes, shoots, or roots no vascular system leaflike structures are present, but lack any vascular tissue early vascular plants are naked, rootless vascularized stems later vascular plants develop vascularized leaves, then roots Reduction in the size of the gametophyte generation wide range of life cycles, some gametophyte dominant, others sporophyte dominant sporophyte generation dependant on gametophyte generation for food; gametophyte is free-living and photosynthetic progressive reduction in size and complexity of the gametoiphyte generation, leading to its complete dependance on the sporophyte for food in angiosperms, 3 celled male gametophyte and a (usually) 8 celled female gametophyte Development of seeds in some vascular plants no seeds seed plants retain the female gametophyte on the sporophyte Spores/Pollen spores for resisting environmental degradation Spores that germinate into the gametophyte generation Spores that germinate into the gametophyte generation or spores that have the gametophyte generation develop within themselves Vascular Plant Groups

 | Back to Top Vascular plants first developed during the Silurian Period , about 400 million years ago.

The earliest vascular plants had no roots, leaves, fruits, or flowers, and reproduced by producing spores. Cooksonia, shown in Figure 8, is a typical early vascular plant. It was less than 15 cm tall, with stems that dichotomously branched. Dichotomous branching (where the stem divides into two ewqual branches) appears a primitive or ancestral trait in vascular plants. Some branches terminated in sporangia that produced a single size of spore. Many scientists now consider "Cooksonia" an evolutionary grade rather than a true monophyletic taxon. Their main argument is that not all stems of Cooksonia-type plants have vascular tissue. The evolutionary situation of a grade would have some members of the group having the trait, others not. The shapes of sporangia on various specimens of Cooksonia also vary considerably. Figure 8. Cooksonia fossil specimen (L) and reconstruction (R). Both Images from . Rhynia, shown in Figure 9, is another early vascular plant. Like Cooksonia, it lacked leaves and roots. One of the species formerly assigned to this genus, R. major, has since been reclassified as Aglaophyton major.

Some paleobotanists consider A. major (Figure 10) a bryophyte, however, it does have a separate free-living sporophyte that is more prominent than the sporophyte, but appears to lack lignified conducting cells. The remaining species, R. gwynne-vaughanii is an undoubted vascular plant. Figure 9. Rhynia gwynne-vaughanii (L) stem cross section from the Rhynie Chert in Scotland. Image cropped and reduced from . (R) Reconstruction of the plant, from . Figure 10. Reconstruction of Aglaophyton major (A-C) and Lyonophyton rhyniensis, another Rhynie Chert plant thought to be the gametophyte of Aglaophyton. Image from the UCMP Berkeley website. Devonian plant lines included the trimerophytes and zosterophyllophytes, which have been interpreted as related to ferns and lycophytes.

The Psilophytes | Back to Top The Division Psilophyta consists of Psilotum nudum (the whisk fern, shown in Figure 11), a living plant that resembling what paleobotanists believe Cooksonia to have been: a naked, photosynthetic stem bearing sporangia. Also in the group is Tmesipteris, which resembles Psilotum except for its possession of smallo vascularized leaves arising on opposite sides of the stem. However, most paleobotanists doubt that Psilotum is a direct descendant of Cooksonia. Molecular studies suggest an affiliation with ferns for Psilotum. Psilotum also has three fused sporangia, termed a synangium, located on the sides of the stems (instead of the tips of stems as in Cooksonia). Figure 11. Psilotum nudum from Hawaii. Note the synangia, the roundish structures on the side of the green stems. Image from . The Lycophytes | Back to Top The next group, the Division Lycophyta, have their sporangia organized into strobili (singular: strobilus).

A strobilus is a series of sporangia and modified leaves closely grouped on a stem tip. The leaves in strobili are soft and fleshy as opposed to the hard, modified leaves in cones. Leaves that contained vascular tissue are another major advance for this group. The presumed evolutionary pathway for the leaf is shown in Figure 12. The leaves in lycophytes, both living and fossil forms, are known as microphylls. This term does not imply any size constraint, but rather refers to the absence of a leaf gap in the vascular supply of the stem at the point where the leaf vascular trace departs. Ferns and other plants have megaphylls, leaves that produce this leaf gap. Figure 12. Proposed steps in the evolution of the microphyll leaf. Note that microphylls do not leave a leaf gap in the stem's vascular cylinder. If we wanted to place Psilotum-like plants on the left top, we would have Lycopodium-like plants on the right top. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission.

Today there are fewer genera of lycophytes than during the group's heyday, the Paleozoic Era. Major living lycophytes include Lycopodium (commonly called the club moss [shown in Figure 13], although it is NOT a moss), Isoetes, and Selaginella (the so-called resurrection plant). Lycopodium produces isospores that germinate in the soil and produce a bisexual gametophyte. These spores are all approximately the same size. Selaginella and Isoetes are heterosporous, and thus produce two sizes of spores: small spores (termed microspores) that germinate to produce the male gametophyte; and larger spores (megaspores) that germinate to produce the female gametophyte. The production of two sizes of spores, and also making separate unisexual gametophytes, is thought an important step toward the seed. Modern lycophytes are small, herbaceous plants. Many of the prominent fossil members of this group produced large amounts of wood and were significant trees in the Carboniferous-aged coal swamps. Figure 13.

Lycopodium venustulum, from from Hawaii. Note the strobili on the tips of the stems, as well as the stems covered with numerous spirally arranged microphylls. Image from . Selaginella is a heterosporous member of the lycophytes. Some species of this genus are able to withstand drying out by going dormant until they are rehydrated. For this reason these forms of the genus are commonly called resurrection plants. An example of this is shown in Figure 14. Figure 14. Selaginella lepidophylla. The top part of the image shows the dried plant, the middle part shows the resurrected or rehydrated plant. Image from . Fossil Lycophytes: Baragwanathia and Drepanophycus Baragwanathia, shown in Figure 15, is an undoubted lycophyte from the middle Silurian deposits of Australia. It has microphyllous leaves spirally attached to the stem, and sporangia clustered in some areas of the plant, although not in terminal strobili as in modern lycophytes. Figure 15.

Left: Reconstruction of Baragwanathia longifolia, from the middle Silurian of Australia. Image from ; Right: Reconstruction of Drepanophycus , a middle Devonian lycophyte. Note the numerous microphyll leaves, placement of sporangia on the upper surface of the sporophylls, and stem anatomy that are all consistent with modern lycophytes. Image from . Drepanophycus is a middle Devonian lycophyte from the Northern Hemisphere, also shown in Figure 15. Its features are very similar to modern lycophytes. Lepidodendron and Sigillaria The Lycophytes became significant elements of the world's flora during the Carboniferous time (the Mississippian and Pennsylvanian are terms used for this time span in the United States). These non-seed plants evolved into trees placed in the fossil genera Lepidodendron and Sigillaria, with heights reaching up to 40 meters and 20-30 meters respectively. Lepidodendron stems are composed of less wood (secondary xylem) that usually is found in gymnosperm and angiosperm trees.

We know much about the anatomy of these coal-age lycopods because of an odd type of preservation known as a coal ball. Coal balls can be peeled and the plants that are anatomically preserved within them laboriously studied to learn the details of cell structure of these coal age plants. Additionally, we have some exceptional petrifactions and compressions that reveal different layers of the plants' structure. Estimates place the bulk, up to 70%, of coal material as being derived from lycophytes. Lepidodendron, pictured in Figures 16 and 17, was a heterosporous lycophyte tree common in coal swamps of the Carboniferous time. As with many large plant fossils, one rarely if ever finds the entire tree preserved intact. Consequently there are a number of fossil plant genera that are "organ taxa" and represent only the leaves (such as Lepidophylloides), reproductive structures (Lepidostrobus), stem (Lepidodendron), spores (Lycospora), and roots (Stigmaria).

Lepidodendron had leaves borne spirally on branches that dichotomously forked, with roots also arising spirally from the stigmarian axes, and both small (microspores) and large (megaspores) formed in strobili (a loose type of soft cone). Lepidodendron may have attained heigths of nearly 40 meters, with trunks nearly 2 meters in diameter. The trees branched extensively and produced a large number of leaves. When these leaves fell from the branches, they left behind them the leaf scars characteristic of the genus. Figure 16. External stem features typical of arborescent lycopods, collectively called lepidodendrids, based on the diamond-shaped "snakeskin" type pattern produced by the helically arranged leaf cushions. On the left is a lower magnification view of this type of pattern, showing the general features of many of these trees. Each leaf abscissed, so that if you are looking, as you are here, at the outside of the stem, you can see a characteristic appearance. On the right is a higher magnification photo showing details of leaf cushions.

Each diamond shaped cushion has a smaller central area called the leaf base where the leaf attached. In the center of the leaf base you can see the leaf trace, or vein to the leaf. The vertical stripe running down each cushion is probably the result of increased girth from secondary cortical growth inside the stem. Images and text from , used with permission of K.B. Pigg, Arizona State University. Figure 17. Top: Cross section through a branch (approximately an inch in diameter) of a large lepidodendrid tree. In the very center is a pith, surrounded by primary xylem and a small fringe of secondary xylem [wood, MJF]. Then there is black gunk and an open white area. Phloem and innermost cortical tissues are typically not well preserved, and this black gunk and white areas probably represent their positions in the branch. The outermost part of the stem is gone. Images and text from , used with permission of K.B. Pigg, Arizona State University. Bottom: Reconstructed diorama of Carboniferous forest scene. Note the ferns and sphenopsids growing around the fallen Lepidodendron trunk, and a large calamite tree in the right foreground.

Image and text from . Sigillaria was another arborescent lycopod, and is also common in coal-age deposits. In contrast to the spirally borne leaves of Lepidodendron, Sigillaria had leaved arranged in vertical rows along the stem. The Sphenophyta | Back to Top The Division Sphenophyta contains once dominant plants (both arborescent as well as herbaceous) in Paleozoic forests, equisetophytes are today relegated to minor roles as herbaceous plants. Today only a single genus, Equisetum, survives. The group is defined by their jointed stems, with many leaves being produced at a node, production of isospores in cones borne at the tips of stems, and spores bearing elaters (devices to aid in spore dispersal). Sporophyte features are seen in Figure 18. The gametophyte is small, bisexual, photosynthetic, and free-living. Silica concentrated in the stems give this group one of their common names: scouring rushes. These plants were reportedly used by American pioneers to scour the pots and pans.

The fossil members of this group are often encountered in coal deposits of Carboniferous age in North America and Europe. Figure 18. Top: A branched species of Equisetum from Hawaii. Note that the branches arise from the same node/area along the stem. Image from . Bottom: Closeup view of the cone of Equisetum hyemale from Hawaii. Note the small leaves at the joints near the lettering in the picture. Image from . The Ferns | Back to Top Ferns reproduce by spores from which the free-living bisexual gametophyte generation develops. There are 12,000 species of ferns today, placed in the Division Pteridophyta. The fossil history of ferns shows them to have been a dominant plant group during the Paleozoic Era. Most ferns have pinnate leaves, exhibiting small leaflets on a frond, as shown in Figure 19. Ferns have megaphyllous leaves, which cause a leaf gap in the vascular cylinder of the stem/rhizome, as shown in Figure 20. The first ferns also appear by the end of the Devonian.

Some anatomical similarities suggest that ferns and sphenophytes may have shared a common ancestor within the trimerophytes. Figure 19. Three genera of the fern family Gleicheniaceae from Hawaii: Upper left: Sticheris owhyhensis, lower left: Diploterygium pinnatum (uluhe lau nui), right: Dicranopteris linearis (uluhe). Image from . Figure 20. Formation of leaf gaps by a megaphyllous leaf. Most plants above the ferns have megaphyllous leaves. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. The Fern Life Cycle The fern gametophyte has both sexes present and is referred to as a prothallium. Prothallia develop from spores shed from the underside of the sporophyte leaves, shown in Figure 21. Once fertilization occurs, the next generation sporophyte develops from the egg located in the prothallium. Figure 21. Sporangia on the underside of Polypodium pellucidum from Hawaii.

Image from . Composite of 4 segmented diagrams of the fern life cycle. Note: to view this in its proper sequence you will need to open your browsert window as wide as possible. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Learning Objectives | Back to Top Be able to discuss the differences in life cycle between vascular and nonvascular plants. Both bryophytes and vascular plants have leaf-like structures. Be able to prepare a single sentence that can tell the reader what a leaf is, as well as what it is not. Both heterospory and homospory impose certain constraints on the gametophyte generation. List some of these. Be able to compare and contrast the typical plant life cycle and a typical animal one. Psilotum is NOT a primitive vascular plant, but rather has more genetic similarity to ferns. What sorts of information might we gather from studying modern Psilotum and its ecology as it relates to Cooksonia and other early vascular plants. What are the chief differences between vascular and nonvascular plants? The fern gametophyte is bisexual.

Speculate on the evolutionary advantages of this in fern colonization of ecologically disturbed areas. Review Questions | Back to Top Which of these plant groups may include the ancestors of plants? a) red algae; b) green algae; c) brown algae; d) fungi ANS is b Plants and their ancestral group share which of the following features? a) chlorphylls a and b; b) strach as a storage product; c) cellulose cell walls; d) all of these ANS is d Vascular plants have ___, specialized cells that help support the plant as well as transport water and nutrients upward from their roots. a) phloem; b) trumpet hyphae; c) xylem; d ) arteries ANS is c The ___ generation of a moss is the dominant phase of its life history. a) sporophyte; b) adult; c) embryo; d) gametophyte ANS is d The lack of conducting cells in bryophytes limits their maximum size to ___.

a) 100 meters; b) 5 cm; c) 1 meter; d) no limit is set by the lack of these cells ANS is b Which of these plants is known only from fossils? a) Cooksonia; b) Lycopodium; c) Equisetum; d) Tmesipteris ANS is a The ___ generation of a fern is the dominant phase of its life history. a) sporophyte; b) adult; c) embryo; d) gametophyte ANS is a ferns Whisk Ferns (Psilotophyta) Club Mosses (Lycophyta) Sporophyte is dominant generation; gametophyte is smaller, but nutritionally independent. Gametophyte forms antheridia and archegonia to produce sperm and egg, respectively. As members of the Plant Kingdom: chl a, chl b, sporic life cycle, starch storage in plastids Vascular Tissue allows upright growth on land large leaves roots for anchorage and absorption of soil minerals and water Control of plant water status: close stomata when transpiration rate exceeds water uptake rate by roots.

Features: 2) eggs in archegonia; sperm in antheridia 3) chl a, chl b, carotenoids, starch, cellulose walls 4) flagellated sperm; water required for fertilization 5) well developed cuticle; functional stomata 6) xylem and phloem 8) independent sporophyte and gametophyte; sporophyte is dominant generation 9) sporophyte can be long lived Sporophyte: Reproduce asexually by growing new leaves out of the rhizome each year Both gametophyte and sporophyte can reproduce asexually by fragmentation Some of the seedless vascular plants produce a strobilus = a step tip with several closely spaced leaves with sporangia. e.g. club mosses, horsetails. Forerunner of the cones of conifers and the flower.

Whisk Fern (Psilotum) no roots; have rhizomes with absorptive rhizoids; mycorrhizae no obvious leaves; sporangia are little balls near stubs where you would expect leaves photosynthetic stems, dichotomous branching Club Mosses (Selaginella, Lycopodium [resurrection fern]) have strobili (the “club” part) some are heterosporus (Selaginella) this group also includes the quillworts (Isotes); some species of quillworts have CAM photosynthesis Horsetails (Equisetum) Equisetum is the only living genus; 15 known species. Silica in the cell walls ==> scouring rush found worldwide in moist habitats, including the damp areas on lower campus near the Social Sciences building Has true stems, roots, and leaves, but the leaves are very reduced. The stem is the primary photosynthetic organ of the sporophyte. Homosporus. The spores have attached elaters. Sporangia in a terminal strobilus.

Ferns the largest group of seedless vascular plants circinate vernation = the curling of young fern leaves (fronds), i.e. “fiddleheads” no strobilus. Spores form on leaves in structures called sori. Some sori are covered by an indusium. The leaves with sori are often called sporophylls. mostly homosporus. Azolla (water fern) is heterosporus.

spore ----> protonema ----> heart-shaped gametophyte with archegonia and antheridia on the underside -----> water required for sperm to swim to egg -----> zygote ----> sporophyte grows attached to gametophyte ----> adult fern sporophyte ----> sporangia clustered in sori on undersides of leaves ----> spores Uses Azolla + Anabaena (a cyanobacterium) - N-fixation in rice paddies Equisetum - scouring various ferns - the floral industry as house plants, ornamentals fossil fuel deposits (from the Carboniferous period, roughly 360-290 million years ago) terminal strobilus Review What are the similarities and differences between the ganetophytes of the bryophytes and the seedless vascular plants? What are the major differences between the four phyla of seedless vascular plants? What similarities are found in the four phyla of seedless vascular plants? What features of seedless vascular plants are found in all members of the Plant Kingdom?

What features of seedless vascular plants are found in all vascular plants but not in the bryophytes (or are not well developed in the bryophytes)? Be familiar with the terminology: homosporus, heterosporus, strobilus, antheridia, archegonia, gametophyte, sporophyte, microspore, megaspore, transpiration, cuticle, stomata, xylem, phloem, circinate vernation, sori, sporophylls How are a spore and a gamete similar? How are they different? Suggested Online Reading What is the conspicuous part of a fern plant called? | Reference.com What is the conspicuous part of a fern plant called? A: Quick Answer The conspicuous part of a fern plant is called the sporophyte. A sporophyte is a mature fern that produces spores. Full Answer The sporophyte consists of three major parts: the fronds (leaves), the rhizome and the sporangia. A mature fern creates spores that are released from sporangia. The sporangia in ferns are typically aggregated into the lines of fern fronds.

In the sporophyte phase of fern reproduction, the spores divide mitotically, producing gametophytes. During fertilization, the union of two gametes produces a diploid zygote. The zygote divides mitotically and forms a new sporophyte. Ferns release spores into the wind. If the spores land somewhere suitable, they eventually grow into a gametophyte. Bryophytes, Ferns and Fern allies Introduction to Bryophytes - Mosses, Liverworts, and Hornworts As we pass from mosses to ferns, we see a gradual transition from primitive to modern traits. There are two major trends you should focus on in today's lab. The first is a transition in life cycles, the second is a change in basic internal structure. First, all plants undergo an alternation of generations, between a haploid gametophyte stage and a diploid sporophyte stage. In the most primitive plants, like mosses, the gametophyte is dominant (i.e. it's big and green). In higher plants like ferns and fern allies, the sporophyte stage is dominant.

Gametophytes produce gametes (sperm and eggs) in a special structure called a gametangium (-ia), while sporophytes produce spores in a special structure called a sporangium (-ia). Second, all plants need to get water to their cells. Primitive bryophytes like mosses and liverworts are so small that they can rely on diffusion to move water in and out of the plant. Mosses have a few strands of water conducting tissue in their central stem, but nothing like the large and well organized network of tubes in tracheophytes, or "tube plants". The vascular tissues in the more advanced ferns and "fern allies" are made up of xylem and phloem, which conduct water, nutrients, and food throughout the plant body. We'll look at these tissues in a later lab. Bryophytes also need a moist environment to reproduce. Their flagellated sperm must swim through water to reach the egg. So mosses and liverworts are restricted to moist habitats. There are no mosses in the desert. But mosses are surprisingly resistant to drying up, and can survive under very harsh conditions.

Mosses are the most abundant plants in both the Arctic and the Antarctic. Asexual reproduction in bryophytes is accomplished by fragmentation or by tiny vegetative "sprouts" called gemmae, which form in special little structures called gemmae cups. Mosses and liverworts are lumped together as bryophytes, plants lacking true vascular tissues, and sharing a number of other primitive traits. They also lack true stems, roots, or leaves, though they have cells that perform these general functions. The leafy green plant that we see when we look at a moss or a liverwort is really the gametophyte, which is the dominant stage in all bryophytes. The sporophytes of bryophytes do not have a free-living existence. They grow directly out of the fertilized egg in the archegonia, and remain dependent on the parent gametophyte for their nutrition.

Characteristics of Divisions Division Bryophyta - (9,500 sp.) - mosses, Mnium, Sphagnum Mosses come in two basic types, a cushiony type, with erect stalks, and a feathery type, which forms flattened mats of low-lying and highly branched moss plants. In both cases, the leafy green gametophytes are dioecious They can be male plants, with antheridia at the top of the plant, or female plants, with archegonia at the top. Remember that these gametophytes are always haploid (1N) plants. Sperm are produced within each antheridium, and an egg in each archegonium. Because the plant is already haploid, these gametes can be created by mitosis, simple cell division. The sperm swims to the archegonia through a thin film of water, drawn by a chemical attractant produced by the female plant, then swims down the neck of the archegonia to the egg. A good morning dew is more than sufficient water for the sperm to swim. Once the sperm enters the archegonia, it fuses with the egg.

The 2N zygote develops into a diploid sporophyte plant, a small stalk that grows directly out of the top of the archegonium. This stalk is initially green, and photosynthetic, but later turns brown and becomes essentially a parasite on the female gametophyte. The sporophyte plant consists of a stalk, and a small capsule on the top. Within the capsule, cells undergo meiosis to produce tetrads of haploid spores. When the capsule is ripe, its hinged lid or operculum opens up, and the spores are quickly dispersed by wind and water. The spores germinate into a tiny green thread, which looks like a simple strand of green algae. This similarity is one more clue that bryophytes are descended from green algae. This early threadlike stage is called the protonema (= first thread, plural = protonemata, like stigma/stigmata). The new adult gametophytes grow from a tiny bud that develops on the protonema. Eventually these gametophytes will grow to produce gametes, and the whole cycle will start over again.

Mosses can also reproduce asexually by fragmentation or by growing little vegetative buds called gemma, which can break off and grow into a new plant . While bryophytes in general are more interesting than important, in the usual sense, a conspicuous exception are mosses of the genus Sphagnum. Sphagnum moss forms dense mats which become compressed into peat, which can be used as fuel, although it’s very smoky. Peat also contains other plants such as reeds, that grow amid the sphagnum. In dried form, peat moss is remarkably absorbent and, and has been used for diapers, for enriching poor garden soils, and as a field dressing for wounds. Whereas cotton absorbs 4-6 times its dry weight, dried sphagnum can absorb 20 times its own weight in fluids! Peat bogs are very important and interesting ecosystems. Sphagnum mosses greatly increase local acidity by releasing H+ ions, and the pH of peat bogs can drop to 4 or lower, perhaps the most acidic natural environment. Peat bogs cover about 1% of the Earth’s land surface, an area about half the size of the United States.

Division Hepaticophyta - (9,000 sp.), liverworts, Marchantia, Conocephalum, Porella Liverworts have the simplest bodies of all the green plants. The gametophyte, the dominant stage, looks like a flat scaly leaf, with prominent lobes. It looks for all the world like a tiny flattened liver, hence the scientific name hepatico-phyta = liver plant. During the Middle Ages, this similarity caused physicians to prescribe liverwort for diseases of the liver. According to the Doctrine of Signatures the Creator had designed all of nature, including plants, with our welfare in mind. People believed that plants had been intentionally designed to resemble the organs of the body they were supposed to heal! Hence liver-wort, wyrt being the Anglo-Saxon word for herb. The shape of the liverwort was the signature of the Creator in nature. Can you guess what walnuts were supposed to cure ? (diseases of the brain) Liverworts share the general properties of bryophytes, but are not very closely related to mosses or hornworts. Many botanists think they may have evolved independently, from a different group of green algae.

For one thing, liverworts don’t store food as starch but as oils. If you get the aquatic liverwort Porella in lab, take a sniff of the jar, but not too deep! It smells of rancid oils, oils that went a little funky while the plant was being shipped. Another characteristic unique to liverworts is their lack of stomata, which are found in all other plants, including mosses and hornworts. In many species of liverworts, such as Marchantia, the one you will most likely see in lab, the antheridia and archegonia are not on top of the plant, but hanging down from the underside of odd little structures that look like tiny umbrellas. (These umbrella-shaped structures are called the antheridiophore and archegoniophore). The bi-flagellated sperm swims to the egg, and fertilization takes place to form a diploid (2N) zygote. The tiny diploid sporophytes, which remain attrached to the parent plant, have a very simple structure. Meiosis within the sporophyte produces a number of haploid spores. These spores are surrounded by curious long and twisted moist cells called elaters.

When the capsule dries and bursts, the elaters twist and jerk around in a way that scatters the spores in all directions. Liverworts can also reproduce asexually by means of special structures called gemmae cups. These little cups can be easily seen on the surface of the plant. Each gemma cup contains a number of tiny plantlets called gemmae, and a single drop of water will disperse them. These little vegetative “clones” will then grow into a new gametophyte. Division Anthocerophyta - (100 sp.), hornworts, Anthoceros The green gametophytes of the hornwort look very much like a liverwort. But their small sporophytes more closely resemble those of mosses. The sporophytes grow out of the gametophyte, and look like a little upright horn. Like mosses, hornworts have stomata, and so are probably more closely related to mosses and other plants than to the liverworts they mat resemble. These plants are symbiotic with the cyanobacteria Nostoc. The cyanobacteria fixes nitrogen for the hornwort.

Taxonomy gemmae cup To Do and View Examine the living mosses on display. Notice the small capsules on top of the tiny sporophytes. Mosses generally grow in one of two growth types: cushiony moss and feathery moss. Examine slides of the antheridia and archegonia. The sausage shaped antheridia produce sperm, and the flask shaped archegonia produces eggs. Examine slides of the moss capsule, and identify the spores. Examine slides of the protonema. What type of algae does it remind you of? This resemblance is additional evidence that green algae gave rise to all higher plants. Examine the terrestrial liverworts Marchantia and Conencephalum (one or both should be on display). How does their growth habit differ from that of the mosses? Can you see any gemmae cups on the upper surface of these plants? Examine slides of the liverwort Marchantia. Examine the aquatic liverworts like Porella and Riccia (one or both should be on display). Notice how they differ from the more terrestrial forms of liverwort.

Look at the preserved liverworts, and observe their distinct reproductive structures (they look like little green umbrellas). How does their life cycle differ from mosses? Examine slides of the hornwort Anthocerophyta. Things to Remember Know the life cycle of the moss in detail, and be able to recognize the various stages. Hint: Be sure you understand the general life cycle of plants, and can tell which stages are haploid gametophytes (1N) or diploid sporophytes (2N). We'll learn several life cycles in lecture and in lab (moss, fern, pine, flowering plant), but all of them are variations on the same basic theme. Ecological, Evolutionary, and Economic Importance Mosses are important in landscaping and gardening, especially peat moss (Sphagnum). Peat moss (Sphagnum) has been used historically as dressings for wounds. Peat moss can be used as fuel. Mosses are the most primitive living land plants. Hornworts contain symbiotic colonies of the cyanobacteria Nostoc. ground pine (Lycopodium) showing strobili The ferns and fern allies germinate from spores.

These plants are mostly homosporous - their spores are identical and you can't differentiate which will grow into male or female plants. They are also monoecious - both the archegonia and antheridia (male and female reproductive structures) are borne on the same plant. Contrast these primitive vascular plants with the more advanced seed plants, the gymnosperms and angiosperms, which germinate from seeds rather than from spores. Seed plants are all heterosporous. It is easy to differentiate the larger female megaspore from the smaller male microspore. The sperm of seed plants have no flagella. They lack antheridia, and only a few still have an archegonia. Unlike the more primitive ferns and fern allies, seed plants are mostly dioecious, having separate male and female plants. In many of these primitive plants, certain leaves are specialized for reproduction. These modified leaves, or sporophylls, bear the sporangia at their bases. These sporophylls usually branch out from a shortened stem, forming a club shaped structure called a strobilus. The pine cone and the flower are elaborate variations on these primitive strobili.

There are four divisions of non-seed tracheophytes, vascular plants that reproduce by means of spores, the Psilophyta, Lycophyta, Sphenophyta, and Pterophyta. Before these non-seed tracheophytes evolved, the bryophytes were the dominant form of plant life. The evolutionary edge of having a more efficient conducting system, and a well-developed root-shoot system enabled them to outcompete bryophytes. If you’re lucky enough to see ground pine or other club mosses growing in the shade of a large pine tree, think for a moment about how these tiny plants were once the masters of the planet, forming vast forests with trunks from 20 to 100 feet tall! Taxonomy Tracheophytes (vascular tissue, no seeds) Division Lycophyta - club moss, quillworts (Lycopodium, Selaginella) Division Sphenophyta - horsetails (Equisetum; fr.L.

equus = horse) Division Psilophyta - whisk fern (Psilotum) Division Pterophyta - true ferns (Pteris; fr.Gr. pteridion = little wing) Terms Characteristics of Divisions Division Psilophyta - (fr Gr. psilo = smooth), whisk ferns, Psilotum There are only two living genera of whisk ferns, sole survivors of a large and widespread group of early land plants. In addition to the living Division Psilophyta, the psilopsids, there are two extinct divisions of primeval vascular plants. The primitive whisk ferns resemble these extinct pioneers in many ways. They are the only living vascular plants that lack a root-shoot system, a characteristic they share with both extinct Divisions of ancestral vascular plants. Some recent molecular evidence suggests that one, or even both, of the living genera of psilopsids may actually be more closely related to ferns, like a fern that has reverted to more primitive traits. If this is true, then Psilophyta will join the ranks of the numerous extinct Divisions of plants. Psilopsids are found in tropical and subtropical areas, and occurs throughout the southern US.

I once found one growing on my back porch under the leaves of a spider plant. Whisk ferns are a common weed in greenhouses all over the world. They are simple green upright stems, with dichotomous branching. They have no leaves, and no true roots. The outer tissues of the stem do all the photosynthesizing. A portion of the stem called a rhizome runs along the ground, or just below it. A rhizome is a horizontal stem that spreads the plant around. Roots grow out the bottom of the rhizome, and a new plant can arise at the same point from the top. The green stem-like plant is the diploid sporophyte, the dominant stage in the life cycle. In the small sporangia (bright yellow) that form along the upper stems, the spore mother cell forms haploid spores by meiosis. Their gametophytes are tiny little thread-like underground plants that lack chlorophyll, and live as heterotrophs in the soil, looking and acting much like a tiny fungi. It actually contains a symbiotic fungi, the same mycorrhizae that live in the rhizomes of the adult sporophyte.

Division Lycophyta - (1,000 sp., fr. Gr. lycos=wolf), club mosses, quillworts, Lycopodium (podus=foot) Their are only five living genera of lycopsids, but at one time from the distant Devonian, about 400 mya, well into the Carboniferous, they were the dominant form of vegetation on the face of the Earth. Now they are reduced to a shadow of their glorious past, inconspicuous little plants in the forest understory. The tropical species are small epiphytes (plants that grow on other plants). Their roots grow from special underground stems called rhizomes, as do most of these primitive tracheophytes. In some species the sporophylls are mixed in with the scale-like leaves. In many species, the sporophylls are organized into strobili, hence the common name of “club moss”. The sperm swim down the strobilus to the archegonia, and the zygote that forms is retained in the cone, which ripens and falls to the ground.

The gametophytes are independent and free-living, They are curious creatures that look and act nothing like their sporophyte parents. They can be either heterotrophic or autotrophic, and usually have a symbiotic fungi associated with them. Many of the lycopsids are heterosporous. Selaginella is a good example of a heterosporous plant. Division Sphenophyta - (15 sp., one genus, fr. Gr. sphen=wedge), horsetails, Equisitum In waste places, disturbed areas like trails and railroad beds, and in odd corners of fields and forests you might find another small plant quietly dreaming of its former splendor, the horsetail. Horsetails appeared in the late Devonian, and were among the dominant forest trees for hundreds of millions of years. Only one genus of Sphenophyta still exists, the genus Equisetum, and it may be the oldest living genus of plants on earth. Horsetails towered among the Carboniferous forests, reaching heights of 30-60 feet.

Much of the coal deposits we exploit for fuel today were formed from horsetails and other trees during the Carboniferous, toward the end of the Paleozoic. Horsetails have true roots, stems, and leaves, though the leaves are little more than flattened stems. Their hollow, ribbed stems are jointed, kind of like a stalk of bamboo, and a whorl of leaves arises at each joint. The plants are spread vegetatively by rhizomes. The stems feel very rough, because the epidermal tissues are impregnated with tiny grains of silica (sand). This probably helps protect the plant against herbivores. These rough stems made this plant ideal for pioneer women to use for scrubbing pots and pans, hence its other common name, “scouring rush”. The green plant we see is the diploid sporophyte generation. The stalks can be highly branched vegetative stalks, which actually look like horse tails, or straight unbranched reproductive stalks, which are tipped with a large strobilus containing the sporangia.

The homosporous spores develop into a teeny-tiny green gametophyte, just a few mm long, that looks like the gametophyte of a fern. The gametophyte is haploid, free-living, and autotrophic. Division Pterophyta - (12,000 sp., fr. Gr. pteridion=little wing), ferns Ferns probably evolved from the psilopsids, sometime in the Devonian, relatively early on in land plant evolution. They are very abundant and diverse, ranging in size from a single centimeter to trees 24 meters tall with 5 meter fronds. Ferns have been better competitors with seed plants than other seedless vascular plants, and are a conspicuous part of the landscape throughout the world, but especially in the tropics, where 75% of their 12,000 species occur. Ferns are relatively advanced plants, with true roots, stems and leaves. The blade of the fern is called a frond, and the little individual leaflets are called pinnae. Ferns have true leaves, what botanists call macrophylls.

While the leaves of more primitive plants, which are called microphylls, are simply extensions of the epidermis of the stem, the leaves of ferns and higher plants were formed as a web of tissue stretched between small terminal branches. The leaves of higher plants, as well as the modified leaves that make up the pine cone and the flower. The life cycle of the fern is typical of other non-seed vascular plants. The leafy green plant is the sporophyte. Fertile fronds develops clusters of small sporangia on the underside of the frond. These clusters of sporangia are called sori (sing. sorus). Sori are often protected by a tiny umbrella-like cap called an indusium (-ia). Ferns are mostly homosporous, though some are heterosporous. The heterosporous state is a more advanced condition, that seems to have evolved independently in several groups of plants. The haploid spores are formed by meiosis inside the sporangium. They are ejected in a miniature explosion caused by the unequal drying of the alternate thick and thin-walled cells that line the outer surface.

The top pulls slowly back until it reaches a critical point and then snaps forward at an incredible speed. At that size scale, the expulsion of fern spores is one of the most explosive events in nature. The spores germinate into tiny gametophytes. The little heart shaped gametophyte is called a prothallus, literally “first-body” (pl prothalli). the prothallus has no vascular tissue. Its small size lets it rely entirely on diffusion. Its tiny rhizoids are associated with mycorrhizal fungi. The little prothallus is green, and photosynthetic, and bears either antheridia and archegonia, or sometimes both together, on its upper surface (lab slides have both on same prothallus). The archegonia are always found at the arch of the heart, and the antheridia are tucked away among the tiny rhizoids at the other end. The sperm swims to the egg to fuse into a diploid zygote. The new sporophyte grows directly out of the top of the gametophyte.

When it first begins to uncurl, the frond looks like the scrolled neck of a violin or fiddle, and this stage of development is called a fiddlehead. To Do and View Examine the living lycopsids on display. Why are they called club mosses? Notice that quillworts and Selaginella are very different in appearance from the club mosses. Examine slides of Selaginella's strobilus. Identify megaspores and microspores. Examine the living horsetails on display. Notice the prominent strobili of the reproductive stalks, and the bushy growth form of the vegetative stalks (if available). Examine the living whisk ferns on display. Psilopsids have a simple dichotomous branching pattern. You may see tiny yellow sporangia on the branches. Whisk ferns lack strobili. These primitive plants are closely related to ferns. Examine the living ferns on display. Can you see any fiddleheads? Look for the rhizomes. Rhizomes are modified horizontal stems bearing roots, that run along or just underneath the ground, and spread ferns and fern allies around.

Examine the living fern prothallus on display under a dissecting microscope. Note its characteristic heart shape. Some prothalli may have a tiny new fern emerging from the notch of the "arch" heart, where the archegonia are located. Examine slides of the prothallus: Find the archegonia (can you see an egg?). Examine the fern leaflet on display under the dissecting microscope. Notice the prominent indusia, and the small sporangia peeking out from beneath. You'll see a few groups of sporangia that have lost their indusium. If you're lucky, as the heat of the microscope dries out the leaflet, you might see the sporangia eject its spores. But don't blink - it's one of the fastest and most explosive acts in nature. Use high power to observe the spores. Examine slides of the sori and indusia; use high power to observe the spores. Things to Remember Know the life cycle of the fern. Recognize specimens and slides of the various stages. Economic, Ecological, and Evolutionary Importance Ferns and fern allies are primarily responsible for our modern deposits of coal.

The fiddleheads of some species of ferns are edible. Ferns are important for the florist, gardening and landscape industries. Consider This Media Resources 24.1 Evolutionary History of Plants The green algae, ancestors of plants, are adapted to living in water while plants are adapted to living on land. Plants have a life cycle in which two multicellular forms alternate. One is the gametophyte (produces gametes) and another is the sporophyte (produces spores). During the evolution of plants, the gametophyte became reduced and dependent on the sporophyte. What are the characteristics of plants? Characteristics of plants (kingdom Plantae) Relationship to algae Ferns and Other Seedless Vascular Plants About Watch and Favorite Watch Watching this resources will notify you when proposed changes or new versions are created so you can keep track of improvements that have been made. Favorite Favoriting this resource allows you to save it in the “My Resources” tab of your account. There, you can easily access this resource later when you’re ready to customize it or assign it to your students.

Ferns and Other Seedless Vascular Plants Ferns, club mosses, horsetails, and whisk ferns are seedless vascular plants that reproduce with spores and are found in moist environments. Learning Objective Identify types of seedless vascular plants Key Points Club mosses, which are the earliest form of seedless vascular plants , are lycophytes that contain a stem and microphylls. Horsetails are often found in marshes and are characterized by jointed stems with whorled leaves. Photosynthesis occurs in the stems of whisk ferns, which lack roots and leaves. Most ferns have branching roots and form large compound leaves, or fronds, that perform photosynthesis and carry the reproductive organs of the plant. Terms Full Text Ferns and Other Seedless Vascular Plants Water is required for fertilization of seedless vascular plants; most favor a moist environment. Modern-day seedless tracheophytes include club mosses, horsetails, ferns, and whisk ferns. Phylum Lycopodiophyta: Club Mosses The club mosses, or phylum Lycopodiophyta, are the earliest group of seedless vascular plants.

They dominated the landscape of the Carboniferous, growing into tall trees and forming large swamp forests. Today's club mosses are diminutive, evergreen plants consisting of a stem (which may be branched) and microphylls (leaves with singular unbranched veins). The phylum Lycopodiophyta consists of close to 1,200 species , including the quillworts (Isoetales), the club mosses (Lycopodiales), and spike mosses (Selaginellales), none of which are true mosses or bryophytes . Lycophytes follow the pattern of alternation of generations seen in the bryophytes, except that the sporophyte is the major stage of the life cycle. The gametophytes do not depend on the sporophyte for nutrients . Some gametophytes develop underground and form mycorrhizal associations with fungi. In club mosses, the sporophyte gives rise to sporophylls arranged in strobili, cone-like structures that give the class its name . Lycophytes can be homosporous or heterosporous .

In the club mosses such as Lycopodium clavatum, sporangia are arranged in clusters called strobili. Phylum Monilophyta: Class Equisetopsida (Horsetails) Horsetails, whisk ferns, and ferns belong to the phylum Monilophyta, with horsetails placed in the Class Equisetopsida. The single genus Equisetum is the survivor of a large group of plants known as Arthrophyta, which produced large trees and entire swamp forests in the Carboniferous. The plants are usually found in damp environments and marshes. The stem of a horsetail is characterized by the presence of joints or nodes , hence the name Arthrophyta (arthro- = "joint"; -phyta = "plant"). Leaves and branches come out as whorls from the evenly-spaced joints. The needle-shaped leaves do not contribute greatly to photosynthesis, the majority of which takes place in the green stem . Silica collects in the epidermal cells , contributing to the stiffness of horsetail plants. Underground stems known as rhizomes anchor the plants to the ground.

Modern-day horsetails are homosporous and produce bisexual gametophytes. Phylum Monilophyta: Class Psilotopsida (Whisk Ferns) While most ferns form large leaves and branching roots, the whisk ferns, Class Psilotopsida, lack both roots and leaves, which were probably lost by reduction . Photosynthesis takes place in their green stems; small yellow knobs form at the tip of the branch stem and contain the sporangia . Whisk ferns were considered an early pterophytes. However, recent comparative DNA analysis suggests that this group may have lost both vascular tissue and roots through evolution and is more closely related to ferns. Phylum Monilophyta: Class Polypodiopsida (Ferns) With their large fronds, ferns are the most-readily recognizable seedless vascular plants. They are considered the most-advanced seedless vascular plants and display characteristics commonly observed in seed plants. More than 20,000 species of ferns live in environments ranging from tropics to temperate forests . Although some species survive in dry environments, most ferns are restricted to moist, shaded places.

Ferns made their appearance in the fossil record during the Devonian period and expanded during the Carboniferous. The dominant stage of the life cycle of a fern is the sporophyte, which consists of large compound leaves called fronds. Fronds fulfill a double role; they are photosynthetic organs that also carry reproductive organs. The stem may be buried underground as a rhizome from which adventitious roots grow to absorb water and nutrients from the soil; or they may grow above ground as a trunk in tree ferns. Adventitious organs are those that grow in unusual places, such as roots growing from the side of a stem. Most ferns produce the same type of spores and are, therefore, homosporous. The diploid sporophyte is the most conspicuous stage of the life cycle. On the underside of its mature fronds, sori (singular, sorus) form as small clusters where sporangia develop . Inside the sori, spores are produced by meiosis and released into the air. Those that land on a suitable substrate germinate and form a heart-shaped gametophyte, which is attached to the ground by thin filamentous rhizoids .

The inconspicuous gametophyte harbors both sex gametangia . Flagellated sperm are released and swim on a wet surface to where the egg is fertilized. The newly-formed zygote grows into a sporophyte that emerges from the gametophyte, growing by mitosis into the next generation sporophyte.

Question: Which is the dominant generation in the ferns?
Answer: Sporophyte